In question 1, it is correct to say 'this person is a professional soccer player' to indicate the person with whom you are acquainted. However, a native speaker of English is more likely to say: 'I am acquainted with a person who is a professional soccer player.' In question 2, it is correct to say 'that person was a professional soccer player'. You are referring to something that was true in the past, and the word 'that' is used to indicate the 'distance' created by the past. So in a present-tense situation you would use 'this' and in a past-tense situation you would use 'that', in the examples given. In question 3, it is correct to say 'this IS bad', because you are talking about something that has just happened. In other words, you are speaking directly from the present tense, from RIGHT NOW. And the response would be: 'Yup, that IS bad', again because the two speakers are responding to something that just happened and is being experienced right at this very moment. In question 4, you would use 'this' in each sentence, for the same reasons I gave in question 1. In question 5 you would use 'that' in each sentence, because you are speaking about a person who is not actually in your presence, but somewhere else, even though you are looking for that person right now in the present. You can apply the 'rules' I have given you in response to your questions to most sentences like this, so I suggest you practice those 'rules' and put your sentences on the italki community website again for further responses. Practice is all you need. Good luck!